Combination spark



March 10, 1964 B. H. MARKS ETAL COMBINATION SPARK PLUG AND ELECTRICALELEMENT Original Filed Jan- 12,' 1960 2 Sheets-Sheet 1 I ll Fm Zluvemoes 6am HMARKS LEONARD J. SPERRY BY 7% 42412-942 ATTORNEY UnitedStates Patent 3,124,718 COMBENATHON SPARK PLUG AND ELECTRECAL ELEMENTBert H. Marks and Leonard J. Sperry, Milwaukee, Wis,

assignors to Globe-Union, Inc., Milwaukee, Wis, a corporation ofDelaware Original application Jan. 12, 196i), er. No. 1,903, now PatentNo. 3,013,131, dated Apr. 27, 1969. Divided and this application Mar.30, 1961, Ser. No. 112,141

3 Claims. (1. SIS-3) This invention relates to spark plugs whichincorporate within their bodies electric circuit elements, andparticularly to such plugs which are essentially no larger than aconventional spark plug and the electric circuit element incorporatedtherein limits the current passing through the center electrode to adaptthe plugs for use in a distributorless ignition system. This applicationis a division of Marks et al. application Serial Number 1,903, filedJanuary 12, 1960.

In a distributorless ignition system where a single power supply iscontinuously connected to a multiplicity of spark plugs it is necessaryto provide current limiting condensers or resistors or inductors inseries with each plug to cause all the plugs to spark simultaneously asstated in Uni ed States Patents No. 2,866,839 and No. 2,866,447. Thesecurrent limiting electric circuit elements have been connected in theelectrical circuit unshielded and physically separated from the sparkplugs and have consequently been subjected to severe moisture,temperature and vibration conditions. There has also resulted increasedradio interference, excessive power loss, spark-over, susceptibility tobreakage, and impractical usage of space.

One object of this invention is to eliminate or minimize the harmful efects of moisture, temperature and vibration encountered by existingsystems in which separate electrical circuit elements are used incircuit with the spark plugs and to reduce the bulk of such systems.

A further object is to insulatively mount an electrical circuit elementwithin a spark plug in a manner which prevents spark-over, excessivepower loss, and susceptibility to breakage.

These objects are accomplished by mounting the electrical circiutelement in a space within the ceramic insulator of a spark plug or byusing such insulator as an integral part of such element. Thus theinsulator provides protection and physical support for the element, andspace requirements are minimized. The element may be cushioned withinthe insulator by an insulating and shock absorbing material to protectit from moisture, vibration and bad effects of temperature. In case theelement is a capacitor, voltage breakdown can be lessened by utilizingpart of the insulator as the dielectric. However, by mounting a unitizedcapacitor entirely within the spark plug insulator the insulatingmaterial will provide adequate voltage breakdown and spark-overprotection from electrode to electrode of the capacitor.

Other objects and advantages will be pointed out in or be apparent fromthe specification and claims, as will obvious modifications of the fourembodiments shown in the drawings of which:

FIG. 1 is a partial sectional view of a spark plug embodying the presentinvention;

FIG. 2 is a sectional view showing another embodiment of the presentinvention;

FIG. 3 is a sectional view showing a third embodiment of this inventionin which a portion of the insulator is not shown;

FIG. 4 is a sectional view of a fourth embodiment of the presentinvention.

The thicknesses of all metalized coatings, silvered sur- 3,124,718Patented Mar. 10, 1964 faces, and bonding pastes are exaggerated in thedrawings for the sake of clarity.

Referring to the drawings, FIG. 1 shows the preferred embodiment of thisinvention in which the center electrode assembly comprises an insulator1d and center electrode 18. The insulator 19 has a bore 12, a firstcounterbore 14 and a second counterbore 16. The center electrode 18 ismounted in bore 12 and has a head 2% which extends into the firstcounterbore 14 to retain electrode 18 in place. Powdered conductiveglass is placed in first counterbore 14 and an electrically conductiveshank 22 having head 24 is pre-pressed into the glass powder. insulatorit) is then heated toaround 1500" Fahrenheit and the shank is pressedinwardly to firmly seat shank head 24 on a tapered shoulder 25 in theinsulator. This provides a hermetic seal between the center electrodeand the insulator.

A metal shell 26 is then applied to the insulator in a conventionalmanner and a ground electrode 27 is properly gapped from the centerelectrode 18.

After the metal shell is applied to the insulator capacitor unitindicated generally at 28 is mounted in counterbore 16. This unitincludes a high-K ceramic slug 30 having silvered ends or electrodes 32and 34. This capacitor is relatively small; about 0.250 inch in diameterand 0.400 inch in length. It may have a rating of from 10 to 50 mmf. Athin copper ribbon 36 is soldered to end 32., and a fiat headed screw 38is soldered to end 34. Screw 38 is screwed into the head of shank 22which is drilled, countersunk and tapped to receive it. The ribbonprojects beyond the end of the insulator 1d. The space in counterbore 16around the capacitor unit is filled with a igh voltage insulatingmaterial to prevent spark-over along the sides of ceramic slug 3i? andalong the counterbore wall. A material found highly desirable for thispurpose is a mixture of silicone oil and uncured silicone rubber. Thismixture is a fairly thin liquid which is poured into counterbore 16. Thespark plug is then heated to cure the silicone material into a resilientrubber capable of withstanding the high temperatures and voltagesencountered in the spark plug stem. Better bonding of the siliconerubber to the bore and ceramic slug walls is secured if a suitableprimer wetting agent is used to coat these walls before pouring thesilicone mixture into counterbore 16.

After the rubber is cured, a terminal unit is bonded to the insulatorstem by adhesive 31. This unit comprises a cap 29 having a centralopening and a threaded terminal 33 having a bore 39. This terminal issecured to the cap with the opening and central bore aligned so thatwhen the unit is placed over the end of the insulator the conductiveribbon 363 is threaded through the terminal. Ribbon 36 is then solderedat 53 to terminal 33 and cut off.

Connection of capacitor unit 28 to terminal 33 as described permits therelative motion between the component parts of the spark plug, caused bythe different coefficients of expansion of the various components, tooccur without damaging the connection between terminal 33 and capacitorunit 28. The stresses ordinarily caused by vibration and relative motionof the parts are relieved by the resilient insulating material. Thecapacitor being mounted within the insulator and hermetically sealedwill not be affected by moisture.

Spark-over along the outside of insulator 10 is pre vented by providingan indentation in the insulator in which silicone rubber washers 37 aremounted.

The center electrode assembly shown in FIG. 2 is constructed similarlyto that shown in FIG. 1. The insulator 47 has a bore 41, a firstcounterbore 43 and a second counterbore 45. A center electrode 19 ismounted in the bore 41 in the same manner electrode 13 is mounted in thebore 12. Powdered conductive glass 15 is placed in first counterbore 43and a headed stud 48 is pressed into the glass powder. These componentsare then heated as previously described to seat the head of the stud 43on the shoulder between the first and second counterbores. A ceramicslug 42 with silvercd ends or electrodes and 56, substantially identicalwith ceramic slug 3%, has its end 46 secured to headed stud byconductive paste 5% or by soldering and its other end 44 is secureddirectly to a threaded terminal 52 by conductive paste 5% or the like.Finely ground mica is compacted around slug 42 and the head of terminal52 and dried. A fluorchemical is then applied to saturate the micathereby providing a good high voltage insulating material indicated as54. The center electrode assembly is next placed in a vacuum and anepoxy seal 56 is made between the terminal 52 and the insulator d7thereby preventing the ingress of air inside the insulator and alsosupporting the terminal. Epoxy resin and silicone material are also goodhigh voltage insulators and may be substituted for the mica andfluorchemical mixture 54.

A capacitor may also be built into the center electrode assembly byusing the insulator itself as the dielectric of the capacitor. In FIG. 3the insulator 6% has a bore 61, a first counterbore 63 and a secondcounterbore 65. An internal electrode 62 is bonded to the inner side ofthe wall of the second counterbore and an external electrode 58 isbonded to the outside of such wall opposite the inner electrode. Acenter electrode 67 is secured in bore 61 and a headed stud 64 is sealedin conductive glass 66 in the manner heretofore described; the head ofstud 64 being in good electrical contact with the electrode 62. A cap 68with a threaded terminal 70 secured thereto fits over the end of theinsulator and is soldered to the electrode 58 to form a seal and aconductive contact therewith. A protective insulating glaze 72 coverselectrode 58 thereby protecting it from deleterious forces andpreventing fiashover to the metal shell in which the assembly ismounted. In order to provide suflicient capacity, the spark pluginsulator 60 must be longer than that used in conventional spark plugs.The increased length is also necessary to provide enough space betweencap 68 and electrode 62 to prevent spark-over. This spacing may beminimized by using insulating material 76 between the cap and electrode62.

In FIG. 4 a center electrode assembly is shown in which the dielectricof the capacitor also is formed by the insulator. In this modification atwo-piece insulator is used which provides an end wall as an additionaldielectric thereby cutting down on the required length of the insulatorand lessening the chances of spark-over. The insulator consists of a toppiece 86 open at only the lower end and a bottom piece 99. The inside ofpiece 86 including its end wall 38 has a metalized coating or electrode78. The outside of piece 86 including its end wall has a metalizedcoating or electrode 82. An insulative coating $8 is applied overelectrode 82 to prevent spark-over along the outside of the insulatorstem. The bottom piece 90 of the insulator has a boss 94 which projectsinto the open lower end of top piece This piece has a bore i l in whicha headed center electrode 92 is sealed with its head projecting from theboss 94 and engaging the electrode 73 when the pieces are assembled asshown.

This construction permits reduction of the length of the insulator toapproximately that of a conventional spark plug due to the increasedcapacity secured from top end A cap 84 with a terminal fits over the endof the insulator and is soldered to the electrode 82. However t.1e endwall 8% completely insulates cap 24 from electrode 73 therebyeliminating the spark-over problem.

Although but four embodiments of the present invention have beenillustrated and described, it will be apparent to those skilled in theart that various changes and modifications may be made therein withoutdeparting from the spirit of the invention or from the scope of appendedclaims.

We claim:

1. In a spark plug of substantially conventional size and shape, aunitary center electrode assembly comprising, an insulator having abore, a center electrode mounted in said bore and projecting from oneend of said insulator, a terminal on the other end of said insulator, acapacitive electrical current limiting element incorporated within saidinsulator and connected in series between said center electrode and saidterminal, said current limiting element including a metallized coatingon a portion of the outer surface of the insulator and a metalizedcoating on a portion of the inner surface of said insulator, said outersurface metalized coating being connected to said terminal, and saidinner surface metalized coating being connected to said centerelectrode, whereby a portion of the insulator itself forms the capacitordielectric.

2. The center electrode assembly according to claim 1 in which saidinsulator is a unitary structure having a central bore with a firstcounter bore for supporting the center electrode and a second counterbore for supporting the metalized coatings.

3. The center electrode assembly according to claim 1 in which saidinsulator is in two pieces, one piece carrying said metalized coatingsand having a closed end, the other piece being adapted for connection tosaid one piece, said other piece carrying said center electrode andholding it in contact with said insulator bore metalized coating.

References Cited in the file of this patent UNITED STATES PATENTS1,317,834 Sweeney Oct. 7, 1919 1,783,525 Stewart Dec. 2, 1930 FOREIGNPATENTS 277,442 Great Britain Sept. 2, 1927

1. IN A SPARK PLUG OF SUBSTANTIALLY CONVENTIONAL SIZE AND SHAPE, AUNITARY CENTER ELECTRODE ASSEMBLY COMPRISING, AN INSULATOR HAVING ABORE, A CENTER ELECTRODE MOUNTED IN SAID BORE AND PROJECTING FROM ONEEND OF SAID INSULATOR, A TERMINAL ON THE OTHER END OF SAID INSULATOR, ACAPACITIVE ELECTRICAL CURRENT LIMITING ELEMENT INCORPORATED WITHIN SAIDINSULATOR AND CONNECTED IN SERIES BETWEEN SAID CENTER ELECTRODE AND SAIDTERMINAL, SAID CURRENT LIMITING ELEMENT INCLUDING A METALLIZED COATINGON A PORTION OF THE OUTER SURFACE OF THE INSULATOR AND A METALIZEDCOATING ON A PORTION OF THE INNER SURFACE OF SAID INSULATOR, SAID OUTERSURFACE METALIZED COATING BEING CONNECTED TO SAID TERMINAL, AND SAIDINNER SURFACE METALIZED COATING BEING CONNECTED TO SAID CENTERELECTRODE, WHEREBY A PORTION OF THE INSULATOR ITSELF FORMS THE CAPACITORDIELECTRIC.